noun, plural: pepsins or pepsine
A proteolytic enzyme in the gastric juice of birds, reptiles, fish, and mammals that partially digest dietary proteins into simpler, shorter chains of amino acids such as proteoses and peptones in the presence of hydrochloric acid.
Pepsin is capable of digesting many proteins from the food except protamine, keratin, and other highly glycosylated proteins. It is converted from pepsinogen that is released from the gastic pits of the stomach. The conversion of pepsinogen into pepsin occurs in the presence of hydrochloric acid or by the action of another pepsin in the gastric juice.
Word origin: Greek pepsis (digestion), from peptein (to digest)